Could've should've would've ¯\_(ツ)_/¯
They could have made it a priority but didnt, they could have designed and tendered the two segments at the same time but didn't. When the Ontario Line was announced, the RLS was preparing the tunneling tenders. The RLN didn't even have a perefered route yet. It was way behind.
Today I noticed something interesting about the
Relief Line Update PDF from Metrolinx. The last slide/Appendix is a collection of photos of "International Examples Of Subway-Level Service". Almost all the examples shown are of metros with shorter and thinner trains than the Toronto TRs. 3 of them are automated lines with rolling stock under 2.7m wide and 100m long. It's as if they knew/planned to derail the Relief Line after studying the RLN project and wanted to replace it with something cheaper/off-the-shelf. This slide would have been comepelty unnecessary if TRs were a done deal at the time.
This is conspiracy theory territory though.